Process of making spark plugs



Feb. 10, 1925.

J. T. LITTLETQN PROCESS OF MAKING SPARK PLUGS Filed April '25, 1921 6 Sheets-Sheet 1 INVENTOR fise T Liitleton/ BY Feb. 10, 1925. 1,525,453

' J. T. LITTLETON PROCESS OF MAKING SPARK PLUGS Filed April 25, 1921 6 Sheets-Sheet 5 INVENTOR Jesse Z Lzttleton BY I ATTORNEY Feb. 10, 1925. 1,525,453

Y J. T. LITTLETON PROCESS OF MAKiNG SPARK PLUGS Filed April 25, 1921 6 Sheets-Sheet 6' INVENTOR 35 Jasze '17 Liazewn vented certain new Patented Feb. 10, 1925.

UNITED STATES PPVATE YORK, ASSIGNOR TO CORNING GLASS WORKS, A CORPORATION OF NEW YORK. I

JESSE T. LITTLETON, OF CORNING, NEW

OF CORNING, NEW YORK,

NIT OFFICE.

PROCESS OF MAKING-SPARK PLUGS.

Application filed April 25,

T 0 all 1072021; z'tmay concern:

Be it known that I, citizen of the United a resident of Cor ments in Processe Jnssn T. LI'ITLETON, a States of America, and ning, New York, have in s of Making Spark Plugs,

of which the following is a specification,

This invention relates to a new and useful construction of sp ark plugs for explosive en-,

0 gines, and to the process of making the same, the object had in view, being the construction of a plug, material of the and shaped around thecentral electrode. spark plugs of this type,

in which glass used'as the insulating core, is formed In it is important to provide for a tight seat between the metallic and glass parts, der the pressures, ture to which the which will not open up unand variations of temperaparts are sub ected in use,

and which will not cause, under the same conditions, strains sufiicient to break the glass core.- plug must possess trical strength, an

In addition to the above the high mechanical and elecd heat resisting properties.

The nature of the problem which is to be solved, will be rendered plainer by a consideration of the following The thermal endurance of core must be low.

facts. the glass of the In. preference a glass whose linear coefficient of expansion is as low as .0000033 perdegree C. is employed.

Metals such as commonly used for heating have a linear coefficient of expansion as high The sparking trode, and the 11 point of the central eleceating near its top, may

reach in use, a temperature as high as 500- I I I n i The compresslon wlthin the engine, and

thus the pressure tending to cause leakage through the plug, may run as high as 720 lbs. to the square These temperat it cements and metallic parts,

. that strains. due t avoided as much and directed tha inch ures and pressures render necessary to I avoid the/use of fusible glazes in uniting glass and and to so dispose the parts 0 heati and cooling are as po'ssi le, or so located t their harmful effect is counteracted or reduced.

This invention eral features her claimed.

further consists in the seveinafter pointed out and and useful Improvei and a shell II'IGII'lbeI".4:,

electrode is preferabl 1921. Serial No. 454,143.

Referring to the accompanying drawin s:

Figure 1, is a side elevation of one form of spark plug embodying this invention;

ig. 2, is a vertical section therethrough;

Fig. 3, is 'a plan view thereof;

ig. 4, is a vertical section through a mold adapted for use in the manufacture of the plug shown in Figs. 1, 2, and 3, the parts being shown assembled and ready for the introduction of a charge of molten glass, the mold plunger being omitted;

Fig. 5, is a vertical section taken on the line 55 of Fig. 4, showing the glass pressed in the mold cavity;

Fig. 6, is a horizontal section through the upper 66 of F 1g. 4.;

Fig. 7, is a horizontai section taken on the line '4 of F ig. v

Fig. 8, is an inverted view of the upper portion of the mold, the parts thereof being separated slightly; p I

Fig. 9, is a detail view in elevationof the central electrode and cap ,1 and Fig. 10, is a view illustrating the method of forming an expansion chamberin the end of the insulating core around the electrode.

s shown in Figures 1', 2 and-3, the improved spark plugforming the subject-matter of this application comprises a central electrode 1, a core 2-, of glass molded around the electrode andinside of'a metallic band 3, in which the band is screwed, and Whichfis adapted to'be screwed into the engine cylinder.

The electrode 1, consists of an upper portion'5, of relativelyv small diameter, which is preferably formed ,ofsome low expansion metal that 'canmbe -sealed vinwthe.glass of which the core. 2nis inader Molybdenum or tungsten are suitable forgthis' part. However, as these metalsfbreakdown when used as spark points, the: lower portion 6 of the made enlarged. in cross section, "and 0 some metal which stands up under-the' 'co "ditions to which the spark points "'al ",Subjected Th e nickelmanganese alloys now in common use are suitable for this; part of the electrode; the two parts of the' electrode'being welded, or otherWisefi-rmly securedtogethe'r. Wiring terminal, in the form of a cap 7, is shown as I I firmly fastened to the upper end of the elec-' trode portion 5. a

The core 2, is, by preference, formed of the lass designated as 15,, in U. S. patent to ullivan and Taylor, No. 1,304,623, of May 27, 1919, having a linear coeflicient of expansion of about .0000033 per degree As will be hereinafter described the glass is molded into form around the central electrode, and within thecap 7, and also within the band 3, which surrounds its central portion, the interior of the band having; rounde annular corrugations 8 therein to anchor the glass within the band. The external contour of the core may closely approach, or be identical with standard practice, including the conical sleeve 9 at the tip whereby a free space is left around the tip and inside of the bushing. An expansion space 10 is formed within the sleeve, around the nickel manganese alloy sparking point 6 of the central electrode to prevent'the cracking of the core 2 by the expansion of the point, which is considerable, under the high temperatures present in use, as such alloys have relatively high expansion; This space at this point is of greater importance, due to the fact that the tapered form of the sleeve 9 (which is desirable to preventthe deposit of carbon and short-circuiting) reduces the resistance of the core to fracture from tensile strain. For this reason, the space 10 should extend back into the corefor a considerable distance and preferably tothe joint between the two sections of the electrode. The variations of temperature at such a point are not.as tip, and the strength of the core (due to its greater cross section) is greater. The junction between the two sections of the central electrode should also be sufliciently removed from the tip of the plug not to melt from the heat of the engine.

The shell 4 may be of an struction, and be provide with any approved form of sparking oint 11.

The spark lug per se 1s claimed in my application erial No. 621,767, filed Feb. 28, 1923.

In the manufacture of a plug such as described, a mold structure, 'such'asshown in the drawings is, by preference used. This structure comprises a base gortion 12, and atop portion 13, that is ma e of separable, and preferably, of hinged halves. The base 12 has in its upper face a recess 14 forming the lower part of the mold cavity. The up or end of this cavity has a diameter sufapproved conficient to receive the lower half of the band 3, a shoulder being formed in the recess 14, immediately below such enlarged diameter, to form a seat for the band. In practice, a block 15 may and the center of this 'block is recessed with a contour to form the tip portion of the core.

- in, is

, form of rectangular support extensive as at the.

the mold is such,,= that the mold in which is placed the 09.

the base 12 be inserted in the,,base 12, of the base 12, a plate 25 4 In order to hold the top portion 13 of the moldain place on the base, the upper surface of the'base surrounding the recess formed into a boss 17, having undercut walls 18, and the top portion 13 has a similarly shaped recess formed in its bottom, and when the two halves of the top portion 13 are assembled together on the base, an locked against separation, the top portion will be firmly anchored on the base.

I The halves of the top portion of the mold are shown as provided with pieces in the blocks 19, that are inserted therein, being held in place by means of screws (see Fig. 8). A layer of insulating material 20, such as mica, is interposed between the contacting surfaces of the blocks and the body of the top portion of the mold. In theblocks 19 is preferably the central recess 16, half of the band 3, and also the lower par of the portion of the cavity forming the core above the band 3. The cavity is extended upwardly above the blocks 19, and its upper portion is adapted to receive an the cap 7 on the upper end of the electrode.

A font cavity 21 is formed in the upper part of the-top portion of the mold, and this cavity communicates by sprue passages 22 with the core cavity, entering the same below the space occupied by the cap 7. In the drawings, these passages are shown as formed in part in the blocks 19.

The construction of the top for receiving the upper ortion of when t e' hinged halves thereof are assembled on. the base, with the metal parts of the spark plug core positioned in the mold cavity, the part of 7, will be separatedby the insulation 20, rom the artthereof in which the band '34s placed, the band being supported by the recess 14 in and the recess 16 formed in the blocks 19 of the top portion of the mold.

The base portion 12 of the mold, below the recess 14 therein, is bored axially of the mold cavity, as at 23, and also bored radial= 1y thereto. In the latter bore is contained a clamping screw 24. i

In forming the core, cap 7 fastened thereon (see Fig. 9) has its lower end inserted in the vertical b on the 'bottom of the base serving to properly position it, and is clamped in place by the screw24. The

the electrode with the 14 there formed lull band 3 is sliped over the upper exeremi y and of the electrode and inserted in the enlarged upper end of the recess 14 in the base 12. The halves of the top portion 13 are then closed around the boss 17 of the base 12.-

The' electrode (which has the lower section 6 thereof made somewhat longer than necessary) now has its lower end firmly held in the base portion of the mold, and its upper end in the top portion. If the base top portions of the mold are now included as a part of an electrical circuit, .fed from a proper source of energy, by means of wires 26 and 27, that are respectively at tached to the top and base, current will flow through the central electrode 1, the insulating layer 20 restraining it to this path. The current should be of sufiicient volume to heat to incandescence the electrode, whereby gases occluded therein will be driven ofl".

After this action has taken place, and while the electrode is still hot, glass which has been placed in the front cavity 21 in any proper way, is forced by the action of a plunger 28 to flow through. .the sprud'passages into the mold cavity formed by. the recesses in the top and base portions of the mold. In doing this, it flows up into the cap 7, and around the electrode, and within the band 3, to which it unites itself by a joint in the nature of a weld.

As the occluded out of the electrode, it will be found that the joint between the electrode and the glass is good, and free of air bubbles which would otherwise-be present and tend to leakage.

The glass having set, the mold is opened and the glass with its surrounding band and the enclosed electrode taken out by means of pliers or other suitable tool and the expansion space 10 then. formed in the tip 0 .the core while the'glass is still hot. One method of forming the space 10 is illustrated by Fig. 10 of the drawings, wherein I have shown the tip of the core being heated in a Meeker gas burner 29, the portion of the electrodeextending beyond the tip being inserted in the burnergauze.

\Vhen the glass forming the tip is sufficiently hot, the body of the core is worked laterally to work -relatively moving such end gases have been drawn the softened glass away from the electrode which is held from such movement by the burner gauze. This motion should preferably be of such character that the expansion space so formed, will extend as far back as-the inner end of the tip section 6 of the electrode, so that strain will not be put on the core by the expansion of such section. The heating of the tip of the core also results in fire-polishing the glassht that point. This fire-polishing has been in itself of value in reducing the tend- 'ency of the spark plug to soot.

The spruce and excess glass in the font cavity are removed by breaking them off and grinding, and the core can now be assembled in the shell 4. In plugs' having short cores, such as the type illustrated, it will be necessary to remove the excess length of the lower portion 6 of the electrode so that its sparking point can be adjusted to the sparking point llof the shell.

Having thus described the nature of this invention. what is claimed is 1. The hereinbefore described method of making a spark plug which comprises the steps of molding a glass core around an electrode, around the lower end of the electrode by of the electrode and the core while the glass forming the lower end of the core is plastic.

2. The hereinbefore described method of making a spark plug which comprises the steps of trode, reheating the tip of the core to render it plastic, and imparting relative lateral movement to the core and tip while the glass is plastic.

3. The hereinbefore described method of making a-spark plug, which comprises the steps of heating an electrode, pressing molten glass around said heated electrode and fire polishing the tipof the core, and cansing relative movement of theelectrode and core during the fire polishing to form a space between the electrode tip and fire polished core tip.

and forming an expansion space molding a glass core around an elec- 1 In testimony whereof, I hereunto sign my A name this 19th day of April 1921.

' i J. T. L TTLE oN. 

